Testosterone manufacturers are being urged to work together on clinical trials that are designed to show whether side effects of low T drugs may increase the risk of heart problems, or whether the medications provide any benefits for men with age-related drops in testosterone levels.

FDA researchers published an article in the New England Journal of Medicine on August 20, highlighting the agency’s concerns over the use of testosterone replacement therapy to address the natural reduction of testosterone levels in men as they age.

The regulatory agency officials calls for the industry to prove that the drugs help men who do not have “classic hypogonadism” without increasing their risk of heart attacks and strokes, indicating that the drug makers should work together on new clinical trials.

The article was written by Dr. Christine P. Nguyen, deputy director of Safety in the FDA’s Office of Drug Evaluation, and other health experts. It comes at a time when questions have been raised about the aggressive marketing of testosterone drugs and concerns over testosterone heart attacks and other potential side effects.

One of the FDA’s major concerns is over the increased use of testosterone by middle-aged and elderly men who have what the FDA calls “age-related hypogonadism.” This is a drop in testosterone levels due to age, which cannot be attributed to classic, and medically provable, causes of hypogonadism, such as pituitary injury, testicular damage or Klinefelter’s syndrome.

In addition, many doctors are prescribing the drugs without even checking to see where their patients’ testosterone levels fall, meaning some may not have low testosterone at all.

In its own research. the FDA found that 28% of men who received new testosterone prescriptions did not appear to have ever been tested for testosterone serum levels. Some experts outside the FDA say that number is even higher.

“Given these patters of use, it appears that a majority of men prescribed testosterone may have age-related hypogonadism rather than classic hypogonadism,” FDA experts warn. “These findings are troubling in light of evidence from recent large observational studies that suggests potential cardiovascular risk associated with testosterone use.”

The FDA announced a warning label update for testosterone therapy in March 2015, indicating that new information would be added about the evidence of a link between testosterone drugs and heart problems. In addition, the agency indicated that use of testosterone therapy should be limited to men diagnosed with hypogonadism, which causes unnaturally low testosterone.

“Given the widespread use of testosterone for age-related hypogonadism, the lack of substantial evidence to support such use, and the unknown effect of the label changes on prescribing patterns, the cardiovascular safety of testosterone products in older men remains an important public health concern. To better determine the effects of testosterone therapy on cardiovascular outcomes among users, the FDA is requiring companies that manufacture these products to conduct a controlled clinical trial,” Nguyen and the others write. “We are encouraging companies to work together on a single trial. We believe the health of American men will be well served byh the presence of accurate drug labels and reliable data to inform clinical decision making.”

There are currently more than 2,000 product liability lawsuits filed by men throughout the U.S. who have suffered a sudden heart attack, stroke, deep vein thrombosis or death while using the popular low T drugs.

All of the complaints involve similar allegations that drug makers manufactured the disease of “low T” through aggressive marketing, resulting in men using the prescription drugs when they had no real medical need. Plaintiffs claim that if the manufacturers had warned about the risk of testosterone health problems, severe and sometimes fatal injuries may have been avoided.

In the federal court system, the testosterone litigation has been centralized as part of an MDL, or Multidistrict Litigation, for coordinated pretrial proceedings.

A small group of Androgel cases are being prepared for trial. Known as “bellwether” cases, a series of six trials are scheduled to begin about one-per-month between October 2016 and April 2017, to help gauge how juries may respond to certain evidence and testimony that is likely to be offered throughout the litigation. While the outcomes of these bellwether trials will not be binding on other cases, they may promote testosterone injury settlements that avoid the need for hundreds of individual trials to be scheduled throughout the U.S.